For mutually joining workpieces made from a synthetic thermoplastic resin, a method for laser welding is known.
Such a conventional laser welding is executed for example as follows. As shown in FIG. 5, a laser-transmissible workpiece 11 is used for one workpiece and for the other workpiece, a laser-absorptive workpiece 13 is used. These workpieces are then put together. A laser 14 is irradiated from the side of the laser-transmissible workpiece 11 towards the laser-absorptive workpiece 13. And the laser 14 transmitted through the laser-transmissible workpiece 11 is absorbed into the laser-absorptive workpiece 13, and then exothermic is caused thereat. The exothermic melts the laser-absorptive workpiece 13 mainly at a laser-absorbing part, and then it melts the laser-transmissible workpiece 11 to weld both workpieces. After cooling, the laser-transmissible workpiece 11 and the laser-absorptive workpiece 13 are joined at a welding position 15.
Merits of the laser welding are feasibility of welding workpieces without any contacts of a laser beam source to workpieces being due to weld; little thermal influence on laser-absorbing neighborhood by local exothermic; no threat of mechanical vibration; feasibility of mutually welding fine parts or workpieces having three-dimensionally complicated structures; excellent reproducibility; feasibility of maintaining sufficient airtightness; excellent welding strength; difficulty of recognizing a boundary line of a welding position by visual observation; no generation of dust and so on.
According to the laser welding, it is not only capable of welding certainly by simple operation but also achieving equal or more welding strength compared with prior methods for joining resin parts. Examples of the prior methods for joining resin parts are clamping by a clamp such as a bolt, a screw, a clip and so on, adhering by an adhesive material, vibration welding, ultrasonic welding and so on. Because of its little vibratory or thermal influence on the laser-welded article, the laser welding also achieves labor saving, improvement of productivity, lowering of production costs and so on. Accordingly, in the automobile industry, the electric industry or the electronic industry for example, the laser welding is practical for joining functional parts or electronic parts that are due to avoid the vibratory or thermal influence thereon. Also the laser welding can be adapted for joining resin parts having a complicated shape.
As a technique of the laser welding, a method for the laser welding is mentioned in Japanese Patent Provisional Publication No. 62-49850. In the method, a laser-absorptive synthetic thermoplastic resin workpiece to which a carbon black that absorbs a laser is added and a laser-transmissible synthetic thermoplastic resin workpiece are piled, and then a laser is irradiated from the side of the laser-transmissible synthetic thermoplastic resin workpiece to weld both workpieces. In this case, the laser-transmissible molded workpiece and the laser-absorptive molded workpiece need to be prepared separately.
In International Publication No. WO2003/039843, another method for the laser welding is mentioned. In the method, a thermoplastic resin molded workpiece A, a thermoplastic resin molded workpiece B and a heat-releasing material C having an infrared transmitting part are in contact in order of C/A/B, and then an infrared ray is irradiated from the side of the heat-releasing material C to weld these workpieces. In this case, it is not necessary to prepare the thermoplastic resin molded workpieces A and B separately, and the workpieces may be formed using similar thermoplastic resin. However, the specific heat-releasing material C must be used in order to adjust the exothermic at the time of laser welding. Therefore, the working process is complicated.
In Japanese Patent Provisional Publication No. 2004-351730, another method for the laser welding is also mentioned. In the method, a joining flange part is respectively preformed as a joint flap for welding on a laser-transmissible resin workpiece and on the laser-absorptive resin workpiece, and the flange parts of each workpiece are butted. Then, a laser is irradiated from the side of the flange part of the laser-transmissible resin workpiece to weld and unify both resin workpieces. In this case, the laser-transmissible resin workpiece and the laser-absorptive resin workpiece need to be prepared separately.